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Discussion Starter #1
Does a bullet really drop then rise when fired?
 

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IMO, its complete BS. Though a shot will be low when fired at 25 yards, I think this has much more to do with the scope being 1 1/2" above the centerline of the bore than a bullet zigzagging. Maybe I'm wrong. I just can't see a bullet going down, then up, then down. I think it's dropping the whole time, and its the angle you view the target at that causes this discrepency.
 

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If a rifle barrel is held level, the bullet begins to fall as soon as it leaves the barrel. Sights or a scope make the shooter raise the barrel from level thereby making the bullet rise and travel in an arch.
 

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BUCKSLAYER15 said:
If a rifle barrel is held level, the bullet begins to fall as soon as it leaves the barrel. Sights or a scope make the shooter raise the barrel from level thereby making the bullet rise and travel in an arch.
That makes perfect sense.
 

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No way does it drop then rise. There was already a good explanation. Hold the barrel level, and the bullet drops immediately. Compensating for this drop to hit a target at 100 yards requires the barrel to be at an angle when shot although sight distance is still level, but above the barrel.
 

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Yeah sorta maybe. The effect of gravity starts pulling a bullet downward as soon as it leaves the muzzle. The shape of the bullet, unless some peculiar airplane wing cross section (which means it is not symetrical) would not rise in that way. It is supposed to be a proven fact that plain balls fired from smooth bore cannon do rise above the line of the bore briefly from spinning forward. What I have been able to duplicate with my small cannon, is that an unpatched 75 caliber steel ball bearing fired from a smooth bore cannon does rise several feet above the bore line by the time it reaches 100yds. No matter how much I leveled the barrel, the balls kept flying over the backstop at Nockamixen (About 25 yrs ago.) I have read references to this effect in Articles about artillery re-enacting, and how dangerous it can be.
 

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applying topspin to a ball is the premise of accurate long range "sniper" barrels in paintball. I have a 18" Dye stainless barrel that is both rifled and the groves are more dense on the top of the barrel producing a ball that spins toward the shooter at the top, this applies a lower pressure above the ball and higher below it and the ball rises (in relation to a standard ballistic trajectory) at a measurable level. the paint marker in question is a Tippmann prolite running CO2 with a MV of 325fps and the thing shoots dang near flat with a red dot out to about 60 yards where it falls off like a brick. but out to that range, paintballs will hit +/- 3" all the way out which goes against anything the ballistics tables say it should do.
 

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applying topspin to a ball is the premise of accurate long range "sniper" barrels in paintball. I have a 18" Dye stainless barrel that is both rifled and the groves are more dense on the top of the barrel producing a ball that spins toward the shooter at the top, this applies a lower pressure above the ball and higher below it and the ball rises (in relation to a standard ballistic trajectory) at a measurable level. the paint marker in question is a Tippmann prolite running CO2 with a MV of 325fps and the thing shoots dang near flat with a red dot out to about 60 yards where it falls off like a brick. but out to that range, paintballs will hit +/- 3" all the way out which goes against anything the ballistics tables say it should do.
 

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Total BS, not opinion, physics.

A bullet drops the instant it leaves the bore and continues to drop the entire time it is flying.

This is why we introduce a up angle to the bore in relationship to the sight, to make the bullet hit where we want it at what distance we want.

Think of it this way, if you had a lazer that was alongside your bore and boresighted perfectly and projected a nice easy to see beam, no matter how you hold your rifle, except straight up, the bullet will fall away from the lazer beam.

Would the bullet be going up if you point the bbl up at a 10deg angle? Yes it will, and it will still be dropping away from the beam, all the time. It goes up because the starting angle drives it up, it does NOT rise. It goes up because of the horizontal force from which it is pushed (shot, thrown) while dropping away from the axis of the bore because of the vertical downward force of gravity.
 

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I believe that the bullet arcs slightly upward and then gradually drops. I always heard that a bullet traveling approximately 2500 fps mv will be at the same point of impact at 25 yds as it wii at 100. From that point on it will drop alot depending on the muzzel velocity. You can look in the back of most reloading manuals and look at the balistic coefficient tables and see the trajectory of most bullets.
 

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Well just when you think common sense prevails, there may be a scientific reason for the contrary. Feast upon this:

In external ballistics
The Magnus effect can also be found in advanced external ballistics. Firstly, a spinning bullet in flight is often subject to a crosswind, which can be simplified as blowing either from the left or the right. In addition to this, even in completely calm air a bullet experiences a small sideways wind component due to its yawing motion. This yawing motion along the bullet's flight path means that the nose of the bullet is pointing in a slightly different direction from the direction in which the bullet is travelling. In other words, the bullet is "skidding" sideways at any given moment, and thus it experiences a small sideways wind component in addition to any crosswind component. (yaw of repose)

The combined sideways wind component of these two effects causes a Magnus force to act on the bullet, which is perpendicular both to the direction the bullet is pointing and the combined sideways wind. In a very simple case where we ignore various complicating factors, the Magnus force from the crosswind would cause an upward or downward force to act on the spinning bullet (depending on the left or right wind and rotation), causing an observable deflection in the bullet's flight path up or down, thus changing the point of impact.

Overall, the effect of the Magnus force on a bullet's flight path itself is usually insignificant compared to other forces such as aerodynamic drag. However, it greatly affects the bullet's stability, which in turn effects the amount of drag, how the bullet behaves upon impact, and many other factors. The stability of the bullet is impacted because the Magnus effect acts on the bullet's centre of pressure instead of its centre of gravity. This means that it affects the yaw angle of the bullet: it tends to twist the bullet along its flight path, either towards the axis of flight (decreasing the yaw thus stabilizing the bullet) or away from the axis of flight (increasing the yaw thus destabilizing the bullet). The critical factor is the location of the centre of pressure, which depends on the flowfield structure, which in turn depends mainly on the bullet's speed (supersonic or subsonic), but also the shape, air density and surface features. If the centre of pressure is ahead of the centre of gravity, the effect is destabilizing; if the centre of pressure is behind the centre of gravity, the effect is stabilizing.
 
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